Measuring the light absorption of a chemical solution is a useful means for detecting and measuring chemicals of interest in the fields of biochemistry, medical diagnostics, and other fields of scientific research. Scientists commonly use the “microplate” as a vessel for holding an array of samples while measuring, or “reading,” their absorption. Microplates typically meet the American National Standards Institute (ANSI) standards developed by The Society for Biomolecular Sciences (SBS) (Danbury, Conn.). These standards describe microplate dimensions in detail including the common 3.3″ by 5″ microplate of 96 sample wells arranged in an 8 by 12 array with an on-center separation of 9.0 millimeters (mm). SBS has formalized ANSI standards for a 384-well microplate (on-center well separation of 4.5 mm) and 24-well microplates (on-center well separation of 18 mm) while other geometries such as 12-well and 48-well plates exist that may not have ANSI standards.
Scientists find it desirable to be able to perform multiple tests on a sample in the same microplate or in the same well of a microplate, for example, in screening blood samples for multiple drugs of abuse. By combining tests on the microplate, the scientist requires a smaller sample volume, consumes less chemical reagents and fewer microplates, and generates less waste. In addition, the scientist may benefit from an overall reduction in preparation time compared to the time required to prepare multiple single-test microplates. Tests can only be combined in the same well if they utilize different reading wavelengths; otherwise, different test results are indistinguishable from one another.
While microplates provide a convenient method of holding a large number of samples, generally, conventional microplate readers and methods for measuring the optical absorption of these samples have one or more shortcomings. For example, several known readers can read at only a single wavelength. Other known microplate readers can read at multiple wavelengths but they cannot perform multiple wavelength-reads simultaneously, increasing the time for each wavelength reading by approximately 100%. Further exacerbating the problem, kinetic assays, i.e., assay tests that require rapid repeated measurements, often exceed the speed capabilities of many current readers. As a result of this speed limitation, known readers are poorly suited to combine kinetic assays within the same microplate. In addition, all multi-wavelength microplate readers of which the present inventor is aware are bulky stationary units that take up large amounts of space, for example, on worktops, and are not easily movable between multiple testing locations and are not easily stored out of the way when not in use.
While many microplate readers offer the capability of thermal control of the microplates, existing readers do not offer a suitable means of testing their ability to maintain a consistent temperature across the microplate. This is particularly a problem for microplate tests such as Endotoxin tests, which are used to measure contaminants in injectable drugs, and which are highly sensitive to temperature variations. Innovative Instruments, Inc. (Wake Forest, N.C.) created their Pyro Pak test device to test for temperature control problems common to microplate readers. Their Pyro Pak device tests for temperature inconsistency across a microplate carrier area but their device is limited to an area representing a few wells of a microplate. Further, the Pyro Pak device is not made of the same material as a microplate which results in a different thermal mass which does not have the same thermal properties as a microplate filled partially or completely with samples. Even if a microplate reader is validated with this test device, there still exists no ability to test if the temperature of an actual microplate with test samples is stable and consistent. For example, a microplate of samples placed on a warm or cool countertop may quickly change temperature unevenly across the microplate, causing an unpredictable shift in the optical results, and no existing microplate reader has the capability of measuring or correcting optical errors resulting from this deviation.